1. Field of the Invention
The present invention relates to an inkjet printing apparatus that ejects a plurality of types of inks and treatment liquid to make contact with the inks, to a print medium thereby printing an image, as well as its printing method.
2. Description of the Related Art
A print medium used for a printing apparatus using pigment inks has an ink absorbing layer on a substrate (not shown) such as paper and film in order to absorb inks. The ink absorbing layer contains a large volume of inorganic fine particles such as silica and alumina that have a high absorption of ink solvent in order to avoid ink feathering and the like. Since gaps among these particles are formed by fine pores of a submicron order, dispersed pigment particles, each having about 100 nm, cannot penetrate inside the ink absorbing layer. Accordingly, a pigment ink layer forming an image is formed on the surface of the ink absorbing layer. As a result, the pigment ink layer is susceptible to abrasion due to an external force. In order to improve abrasion resistance, treatment liquid is ejected onto the surface layer of the pigment ink layer to form a transparent coating layer, thereby reducing a coefficient of dynamic friction of an image surface. Japanese Patent Publication No. 3190535 discloses that in a multipass printing apparatus that prints an image to a predetermined region of a print medium, the image is formed by ejecting ink with the use of a print head, and treatment liquid is applied to an ink layer from the print head during at the last scan of the print head.
If an excessive volume of treatment liquid is applied to the pigment ink layer by one scan, drying tends to be insufficient, and the surface of the coating layer formed by the treatment liquid becomes a mirror surface, which may cause an interference pattern and deteriorate an image grade.
Meanwhile, in order to facilitate drying of treatment liquid, it is considered that a volume of treatment liquid applied by one scan is reduced and treatment liquid is applied to a pigment ink layer by a plurality of scans. However, in such a case, the surface of the coating layer formed by the treatment liquid becomes irregular, which may cause an image to have an insufficient glossiness and an uneven glossiness.